证明:∵BD,B′D′是高,∴ΔABD和ΔA′B′D′都是直角三角形
∵ AB=A′B′,BD=B′D′∴RtΔABD≌RtΔA′B′D′
∴∠BAC=∠B′A′C′∵AC=A′C′∴ΔABC≌ΔA′B′C′